One of the bottlenecks in structural studies of HIV-host complexes has been an incomplete picture of the repertoire of interactions. Without appropriate host partners, many of the HIV proteins do not adopt folded structures or exist in alternative conformations, particularly in cases where the viral protein interacts with more than one host complex. To address this problem, the HARC Center performed a comprehensive analysis of HIV-human protein-protein interactions (PPIs) using affinity-tagged HIV proteins expressed in both HEK293 and Jurkat T cell lines. By combining affinity purification/mass spectrometry (AP-MS) with a novel scoring algorithm, termed MiST, 497 high confidence HIV-human PPIs involving 435 human factors were identified. Among the PPIs'' found, we recapitulated many known HIV-human physical interactions, but the vast majority has not been previously described. Many of these are presently being followed up in the context of the HARC Center as well as collaboratively with outside groups with expertise in particular systems. For example, a collaboration between Krogan, Gross, and Reuben Harris (U. Minn.) identified CBF|3 as a new component of the Vif ubiquitin ligase complex that is essential for Vif function in the virus and stabilizes the complex in vitro, thereby allowing structural investigations of Vif to proceed (see Vif project). A collaboration between Krogan and Craik demonstrated that PR interacts with and cleaves the elF3d subunit of the elF3 translational initiation complex, a protein that inhibits HIV replication (see PR project). An exciting cross-Center collaboration between Krogan and Wes Sundquist (CHEETAH) has found that several Gag interactors play significant and unexpected roles in HIV infection and already has led to the crystal structure of one new factor.